Stable electrolyte matrix for molten carbonate fuel cells

ABSTRACT

A method of making an electrolyte matrix includes: preparing a slurry comprising a support material, a coarsening inhibitor, an electrolyte material, and a solvent; and drying the slurry to form an electrolyte matrix. The support material comprises lithium aluminate, the coarsening inhibitor comprises a material selected from the group consisting of MnO2, Mn2O3, TiO2, ZrO2, Fe2O3, LiFe2O3, and mixtures thereof, and the coarsening inhibitor has a particle size of about 0.005 μm to about 0.5 μm.

STATEMENT OF GOVERNMENT RIGHTS

This invention was made with U.S. Government support under EnergyEfficiency & Renewable Energy Award No. DE-EE0006606 awarded by theDepartment of Energy. The U.S. government has certain rights in thisinvention.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. patent applicationSer. No. 15/343,864, filed Nov. 4, 2016, which is hereby incorporated byreference herein in its entirety.

BACKGROUND

The present disclosure relates to matrices for supporting an electrolytein a molten carbonate fuel cell.

Molten carbonate fuel cells (MCFC) are of great interest for powergeneration, due to their high efficiency and clean conversion ofchemical energy into electric energy. Generally carbonate fuel cellsoperate at intermediate temperatures (575° C.−650° C.) and employcarbonaceous fuels containing carbon dioxide and carbon monoxide. Atypical carbonate fuel cell assembly may include a porous Ni anodestabilized against sintering by Cr and/or Al additives and a porousin-situ oxidized and lithiated NiO cathode. The anode and cathode may beseparated by a molten alkali carbonate electrolyte, such as Li₂CO₃/K₂CO₃or Li₂CO₃/Na₂CO₃, contained within a porous ceramic matrix, such asLiAlO₂.

The electrolyte matrix, sandwiched between the electrodes, serves toisolate the fuel from the oxidant, store electrolyte, and facilitateionic transport. The electrolyte matrix may be a micro-porous ceramicstructure that retains a liquid electrolyte by capillary force. AnLiAlO₂ powder (α or γ-phase) is a common material used as a basic matrixsupport. During the operation of a MCFC, the capacity of the matrix tohold electrolyte by capillary force may be altered due to a change inthe properties of the LiAlO₂ particles that make up the matrix. Severalstudies have shown the growth of LiAlO₂ particles during long term celloperation, leading to the formation of large pores with a size greaterthan 0.6 μm. This growth produces a decrease in the electrolyteretention ability of the matrix, which may increase the electrolyte lossrate and gas cross-over negatively impacting the cell performance. Thus,it would be advantageous to provide an electrolyte matrix with anenhanced stability that increases cell life and maintains stable cellperformance.

SUMMARY

In certain embodiments, an electrolyte matrix is provided. Theelectrolyte matrix includes a support material comprising lithiumaluminate, an electrolyte material comprising lithium carbonate, and acoarsening inhibitor. The coarsening inhibitor comprises MnO₂, Mn₂O₃,TiO₂, ZrO₂, Fe₂O₃, LiFe₂O₃, or mixtures thereof, and the coarseninginhibitor has a particle size of about 0.005 nm to about 0.5 μm.

In one aspect, the coarsening inhibitor that has a BET surface area ofabout 10 m²/g to about 50 m²/g.

In one aspect, the coarsening inhibitor has a BET surface area of about20 m²/g to about 40 m²/g.

In one aspect, the coarsening inhibitor has a BET surface area greaterthan or equal to the BET surface area of the support material.

In one aspect, the support material has a surface area of about 10 m²/gto about 24 m²/g.

In one aspect, the coarsening inhibitor is present in an amount of about0.1 vol. % to about 40 vol. % of the electrolyte matrix.

In one aspect, the electrolyte matrix further comprises a binder.

In one aspect, the electrolyte matrix further comprises a reinforcingmaterial.

In one aspect, the coarsening inhibitor has a different crystalstructure than the support material.

In aspect, the electrolyte matrix is substantially free of pores with asize of 0.6 μm or greater.

In other embodiments, a method for making an electrolyte matrix isprovided. The method comprises preparing a slurry comprising a supportmaterial, a coarsening inhibitor, an electrolyte material, and asolvent, and drying the slurry to form an electrolyte matrix. Thesupport material comprises lithium aluminate. The coarsening inhibitormaterial comprises MnO₂, Mn₂O₃, TiO₂, ZrO₂, Fe₂O₃, LiFe₂O₃, or mixturesthereof. The coarsening inhibitor has a particle size of about 0.005 μmto about 0.5 μm.

In one aspect, preparing the slurry comprises an attrition millingprocess that reduces the size of the materials in the slurry.

In one aspect, the method further comprises tape casting the slurrybefore drying the slurry.

In one aspect, the method further comprises adding a binder, aplasticizer, a reinforcing material, or a combination thereof to theslurry.

In one aspect, the coarsening inhibitor is present in an amount of about0.1 vol. % to about 40 vol. % of dry components of the slurry.

In other embodiments, an electrolyte matrix is provided. The electrolytematrix comprising a support material and an electrolyte materialcomprising lithium carbonate. The support material comprises lithiumaluminate and MnO₂, Mn₂O₃, TiO₂, ZrO₂, Fe₂O₃, LiFe₂O₃, or mixturesthereof as a dopant in the lithium aluminate.

In one aspect, the dopant is present in the lithium aluminate in anamount of about 0.1 mol. % to about 15 mol. %.

In one aspect, the support material has a surface area of about 10 m²/gto about 24 m²/g.

In one aspect, the electrolyte matrix further comprises a binder.

In one aspect, the electrolyte matrix further comprises a reinforcingmaterial.

In one aspect, the electrolyte matrix is substantially free of poreswith a size of 0.6 μm or greater.

In other embodiments, a method of making an electrolyte matrix isprovided. The method comprising forming a mixture of an aluminumcontaining precursor, a lithium containing precursor, and a dopantprecursor; drying the mixture to form a powder; heat treating the powderat a temperature of about 550° C. to about 800° C. for a period of about6 hours to about 30 hours to form a lithium aluminate including adopant; preparing a slurry comprising the lithium aluminate including adopant, an electrolyte material, and a solvent; and drying the slurry toform an electrolyte matrix. The dopant precursor is in oxide or saltform, and the dopant comprises MnO₂, Mn₂O₃, TiO₂, ZrO₂, Fe₂O₃, LiFe₂O₃,or mixtures thereof.

In one aspect, the dopant precursor comprises MnO₂, TiO₂, ZrO₂, Fe₂O₃,or mixtures thereof.

In one aspect, the aluminum precursor comprises Al₂O₃.

In one aspect, the lithium precursor comprises lithium carbonate.

In one aspect, the method further comprises tape casting the slurrybefore drying the slurry.

In one aspect, the method further comprises adding a binder, aplasticizer, a reinforcing material, or a combination thereof to theslurry.

In one aspect, the lithium aluminate including a dopant comprises thedopant in an amount of about 0.1 mol. % to about 15 mol. %.

In other embodiments, a fuel cell is provided. The fuel cell comprisesany of the electrolyte matrices described herein.

These and other advantageous features will become apparent to thosereviewing the disclosure and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows X-Ray Diffraction (XRD) patterns for an LiAlO₂ matrixmaterial and a ZrO₂ doped LiAlO₂ obtained by heat treatment of a mixtureof Zr(OH)₄, Al₂O₃ and Li₂CO₃, according to an embodiment of the presentinvention.

FIG. 2A shows a scanning electron microscope (SEM) image of aZrO₂—LiAlO₂ matrix material obtained by heat treatment of a mixture ofZr(OH)₄, Al₂O₃ and Li₂CO₃ at 680° C. to 850° C. for 12 to 30 hours,according to an embodiment of the present invention.

FIG. 2B shows the image of FIG. 2A with the ZrO₂ material highlighted aslight regions.

FIG. 3 shows an Energy Dispersive X-Ray Spectroscopy (EDX) spectrum forthe material shown in FIGS. 2A and 2B.

FIG. 4 shows the variation of the resistance of a matrix of the presentinvention relative to a conventional matrix as a function of servicelife.

FIG. 5 shows the fraction of large pores, greater than 0.2 μm, presentin a matrix of the present invention and a conventional matrix as afunction of service life.

DETAILED DESCRIPTION

The electrolyte matrices of the present invention exhibit reducedlithium aluminate (LiAlO₂) coarsening, thereby maintaining a higherelectrolyte retention ability and more consistent performance duringoperation. The electrolyte matrices achieve this reduced coarseningbehavior due at least in part to the presence of a coarsening inhibitorin the electrolyte matrices. The coarsening inhibitor may be present inthe form of discrete particles in the electrolyte matrices or as adopant within a support material of the electrolyte matrices.

The electrolyte matrices are capable of maintaining an appropriateelectrolyte fill level over a useful life of at least 5 years. Theuseful life of an electrolyte matrix may depend on multiple factors,such as the pore sizes present at the beginning of life and thecoarsening rate. The electrolyte matrices disclosed herein may have apore size of less than 0.2 μm at the beginning of life, and a lowcoarsening rate. The coarsening rate may be influenced by factorsincluding the rates of solubility, diffusion, and precipitation of theLiAlO₂.

The particle coarsening of LiAlO₂ that occurs during operation of amolten carbonate fuel cell may occur through the Oswald ripeningprocess. The coarsening includes the dissolution and subsequentprecipitation of LiAlO₂. This coarsening process is diffusioncontrolled, and may be mitigated by increasing the diffusion distance.One strategy for increasing the diffusion distance includes mixingparticles of different crystal structures in the electrolyte matrix, asthe dissolved species have a longer distance to travel beforeencountering a material with the same crystal structure on which theymay precipitate.

In one embodiment, a heterogeneous electrolyte matrix material isprovided. The heterogeneous matrix material may include a supportmaterial and a coarsening inhibitor. Each of the components of theheterogeneous matrix material may be present as discrete particles.

The support material may be any appropriate electrolyte supportmaterial, such as LiAlO₂. The LiAlO₂ support material may be in the γ orα form. The support material may have a Brunauer-Emmett-Teller (BET)surface area of about 10 m²/g to about 24 m²/g. The support material mayhave an average particle size of about 0.1 nm to about 100 nm.

The coarsening inhibitor may be any material that has a differentcrystal structure than the support material and exhibits good stabilityin a carbonate electrolyte. The coarsening inhibitor may be an oxidematerial, such as MnO₂, Mn₂O₃, TiO₂, ZrO₂, Fe₂O₃, LiFe₂O₃, or mixturesthereof. The coarsening inhibitor may have an average particle size inthe range of about 0.005 μm to about 0.5 μm. The particle size may referto a diameter or equivalent diameter of the coarsening inhibitorparticles. The small average particle size of the coarsening inhibitorenhances the degree of contact between the coarsening inhibitor and thesupport material. The coarsening inhibitor particles may have anyappropriate geometry, such as spherical particles, rounded particles,elongated particles, or irregularly-shaped particles.

The coarsening inhibitor may have a BET surface area that is equal to orgreater than the BET surface area of the support material. The BETsurface area of the coarsening inhibitor may be about 10 m²/g to about50 m²/g, such as about 15 m²/g to about 50 m²/g, or about 20 m²/g toabout 40 m²/g. In the event that the BET surface area of the coarseninginhibitor is too low, the contact between the coarsening inhibitor andthe support material may not be sufficient to produce the desiredreduction in the coarsening of the support material.

The coarsening inhibitor may be present in the electrolyte matrix in anyamount sufficient to reduce the coarsening of the support material whileavoiding negative effects on the performance of the fuel cell. Thecoarsening inhibitor may be present in the electrolyte matrix in anamount of about 0.1 vol. % to about 40 vol. % of the dry components ofthe electrolyte matrix, such as about 0.1 vol. % to about 10 vol. %, orabout 5 vol. % to about 15 vol. %. The coarsening inhibitor may bepresent in the electrolyte matrix in an amount of about 1 wt. % to about40 wt. %, such as about 10 wt. % to about 20 wt. %. In the event thatthe coarsening inhibitor is too low, the coarsening of the supportmaterial may not be reduced. If the coarsening inhibitor content is toohigh, the performance of the fuel cell may be negatively impacted andthe electrolyte chemistry may become too basic.

The electrolyte matrix may optionally include reinforcing materials thatserve to increase the compressive strength, crack resistance, andthermal cycle capability of the electrolyte matrix. The reinforcingmaterials may have any appropriate geometry, such as particles orfibers. Particles of reinforcing material may have a spherical shape,rounded shape, or disk shape. The reinforcing material may be formed ofany appropriate composition, such as a metal or oxide material. Thereinforcing material may be a coarse material, such as particles with asize of about 10 μm to about 120 μm. In some embodiments, thereinforcing material may include aluminum oxide (Al₂O₃).

The electrolyte material may optionally include a binder. The binder maybe a sacrificial binder that is removed at high temperatures, such asthe conditioning temperatures of a molten carbonate fuel cell. In someembodiments, the binder may include a polymeric material.

The electrolyte present in the electrolyte matrix may include anyappropriate carbonate. In some embodiments, the electrolyte may includelithium carbonate (Li₂CO₃). The electrolyte may also optionally includesodium carbonate or potassium carbonate.

The electrolyte matrix may be substantially free of large pores. In someembodiments, the electrolyte matrix may be substantially free, or free,of pores with a size greater than or equal to about 0.6 In some otherembodiments, the electrolyte matrix may be substantially free, or free,of pores with a size greater than about 0.2 The electrolyte matrix maybe substantially free, or free, of pores with a size greater than orequal to about 0.6 μm after operation of a fuel cell. In someembodiments, the pore structure of the electrolyte matrix may be free ofpores with a size greater than about 0.2 μm after the burnout of abinder.

The heterogeneous electrolyte matrix may be made by any appropriateprocess. In some embodiments, a heterogeneous electrolyte matrix may beproduced by a process including forming a slurry containing a supportmaterial, coarsening inhibitor, electrolyte material, and a solvent. Theslurry may then be dried to form the electrolyte matrix. The supportmaterial, coarsening inhibitor, and electrolyte material may be any ofthose described herein. The solvent may be any appropriate solvent, suchas methyl ethyl ketone (MEK), or a mixture of MEK, cyclohexane, and fishoil.

The slurry may be formed by an attrition milling process, such as ballmilling. The milling process may be continued until a desired particlesize is achieved. The grinding media may have a ball size of 0.3 mm to 3mm, and may have a loading of about 60% to about 80%. The milling speedmay be about 2,000 rpm to about 3,000 rpm. After the desired particlesize is achieved, optional components may be added to the slurry, suchas a reinforcing material, binder, plasticizer, or pore formingmaterial.

The slurry may include the coarsening inhibitor in any appropriateamount. In some embodiments, the coarsening inhibitor may be present inthe slurry in an amount of about 0.1 vol. % to about 40 vol. %, such asabout 0.1 vol. % to about 10 vol. %, on the basis of the dry componentsof the slurry.

The slurry may be dried by any appropriate process. In some embodiments,the slurry may be tape cast, such as with a doctor blade, and then driedto form an electrolyte matrix. The drying may take place at atemperature of about 25° C. to about 30° C. for about 30 minutes toabout 50 minutes. The dried electrolyte matrix may then optionally cutto a desired size before being installed in a fuel cell.

In another embodiment, the electrolyte matrix may include a homogeneousdistribution of support material and dopant. The support material may belithium aluminate, as described above. The support material may have asize, surface area, and shape as described above. The dopant may be anyof the coarsening inhibitors described above. The dopant may be in theform of uniformly distributed fine particles on or near the surface ofthe support material particles, such as particles with a size of lessthan about 0.1 μm. The dopant particles may have any appropriategeometry, such as rounded particles, spherical particles, or elongatedparticles. The dopant may be supported on the support material such thatthe support material and dopant may act as a single particulatematerial. In some embodiments, the dopant may be present in the crystalstructure of the support material.

The dopant may be present in any amount sufficient to suppress thecoarsening of the support material. In some embodiments, the dopant maybe present in an amount of about 0.1 mol. % to about 15 mol. % relativeto the support material.

The electrolyte matrix may further include optional components. Theoptional components may include a reinforcing material, binder,plasticizer, or pore forming material as described above. Theelectrolyte included in the electrolyte matrix may be a carbonate, asdescribed above.

The electrolyte matrix that includes a homogeneous distribution ofsupport material and dopant may be produced by any appropriate process.In some embodiments, dopant precursors made be added to a synthesismixture for the synthesis of the support material. The synthesis mixturemay include aluminum precursors, lithium precursors, and dopantprecursors, and may be an aqueous mixture. The synthesis mixture maythen be dried to form a powder, and the powder may be heat treated toform a support material including a dopant. The support materialincluding a dopant may then be included in a slurry as described aboveto form an electrolyte matrix, with the presence of an additionalcoarsening inhibitor in the slurry being unnecessary. In someembodiments, the support material including a dopant may be formed intoan electrolyte matrix that includes a coarsening inhibitor in additionto the dopant.

The aluminum precursors and lithium precursors may be any materials thatare capable of forming a lithium aluminate support material, and may bepresent in amounts appropriate to form a lithium aluminate supportmaterial. The aluminum precursors may include aluminum hydroxide,alumina, aluminum isopropoxide, or aluminum isobutoxide, with aluminabeing preferred. The lithium precursors may include lithium hydroxide,lithium oxide, lithium acetate, or lithium carbonate, with lithiumcarbonate being preferred.

The dopant precursors may be any precursor capable of forming thedesired dopant species. In some embodiments, the dopant precursor mayinclude MnO₂, Mn₂O₃, Fe₂O₃, TiO₂, or ZrO₂. The dopant precursor mayalternatively be salts of manganese, iron, titanium, or zirconium. Insome embodiments, the dopant precursor may be a hydroxide, such aszirconium hydroxide.

The synthesis mixture of including the support material precursors andthe dopant precursors may be formed by any appropriate process. In someembodiments, the synthesis mixture may be formed by subjecting anaqueous mixture of an aluminum precursor, lithium precursor, dopantprecursor, and a dispersant to an attrition milling process. The solidloading of the milled mixture may be about 5 wt. % to about 30 wt. %.The conditions of the attrition milling process may be similar to thosedescribed above.

The synthesis mixture may be dried by any appropriate process to form apowder. In some embodiments, the mixture may be spray dried. The mixturemay alternatively be dried in air at about 80° C. to about 160° C. for aperiod of about 6 hours to about 12 hours, such as overnight.

The dried powder may then be subjected to a heat treatment sufficient toform lithium aluminate. The heat treatment may be at about 550° C. toabout 800° C., for a period of about 6 hours to about 30 hours. Theresulting lithium aluminate includes a uniformly dispersed dopant, inthe form of particles with a size of less than 0.1 μm and a BET surfacearea of at least about 15 m²/g to about 30 m²/g. The resulting lithiumaluminate may also be doped with a small amount of the metal componentof the dopant precursor, such that the lithium aluminate is more stableagainst phase transformations.

The electrolyte matrices described herein may be employed in any moltencarbonate fuel cell. The electrolyte matrices may be disposed between aporous anode and a porous cathode. The porous anode may be nickelstabilized against sintering by the addition of chromium and/oraluminum. The porous cathode may be in-situ oxidized and lithiatednickel oxide.

The electrolyte matrices described herein exhibit improved performance.The electrolyte matrices may reduce particle coarsening and theresulting population of large pores by greater than 60% during celloperation in comparison to equivalent lithium aluminate electrolytematrices that do not include coarsening inhibitor additives. Theelectrolyte matrices also do not exhibit a phase transformation undermolten carbonate fuel cell operation conditions. The electrolytematrices also exhibit greater than a 40% improvement in resistancestability compared to a baseline of an electrolyte matrix that does notinclude a coarsening inhibitor additive. The electrolyte matrices alsoexhibit improved electrolyte filling compared to a baseline of anelectrolyte matrix that does not include a coarsening inhibitoradditive, possibly due to an enhanced capillary force.

Exemplary Embodiments

A LiAlO₂ powder was obtained by heat treating a spray dried mixtureprepared from an aqueous slurry containing Zr(OH)₄, Al₂O₃, and Li₂O₃ ata temperature of 680° C. to 850° C. for between 12 hours and 30 hours.An X-Ray Diffraction (XRD) pattern of the powder is shown in FIG. 1, anddemonstrates that the powder includes both LiAlO₂ and ZrO₂ phases. AScanning Electron Microscope (SEM) image of the powder is shown in FIG.2A, and a modified SEM image highlighting ZrO₂ is shown in FIG. 2B. Asshown in FIG. 3, an Energy Dispersive X-Ray Spectroscopy (EDX) spectrumdemonstrates that ZrO₂ powder is uniformly distributed within the LiAlO₂support material.

A matrix support material (LiAlO₂) was mixed with an MO₂ coarseninginhibititor additive (M=Zr, Mn, Ti or Fe) and Li₂CO₃ and milled togetherto achieve the desired average particle size. The milling/mixing wasperformed in a solvent, such as MEK or a mixture of MEK and cyclohexanewith 1 to 5 wt % of fish oil to prevent re-agglomeration of particles.An attrition milling technique using a grinding media having 0.3 mm to 3mm ball size was used to mill the mixture of LiAlO₂, MO₂ and Li₂CO₃. Thegrinding media loading varied between 60% and 80% and the grinding speedwas between 2000 rpm and 3000 rpm. After achieving the desired particlesize, aluminum particles were added to the milled mixture of LiAlO₂,Li₂CO₃ and MO₂. The amount of MO₂ additive was between 0.1 vol. % and 40vol. %, with an amount between 0.1 vol. % and 10 vol. % achieving thedesirable results in terms of particle coarsening reduction.

In the next step, additives, including a binder and a plasticizer, wereadded to the slurry. In this example, approximately 19 wt. % to 21 wt. %of Acryloid binder and Santicizer® 160 plasticizer were used as theadditives. The slurry was then tape cast using a doctor blade and driedat a temperature between 25° C. and 30° C. for a time of 30 minutes to50 minutes to form green sheets. The green sheets were then laminatedand tested in single cells for a performance and life stabilityevaluation.

Several bench-scale, single cells (250 cm²) were tested to determine theperformance and stability of the electrolyte matrix. Each single cellassembly included a porous Ni—Al and/or Ni—Cr anode and a porous in-situoxidized and lithiated NiO cathode, separated by the electrolyte matrix.A comparative example included an electrolyte matrix that of LiAlO₂ inthe absence of a coarsening inhibitor additive. The cathode (250 cm²)was filled with an appropriate amount of Li/K or Li/Na electrolyte andan appropriate amount of Li/Na or Li/k electrolyte was also stored inthe cathode current collector to achieve the necessary electrolytebalance.

The anode gas for the test was 72.8% H₂-18.2% CO₂-9% H₂O and the cathodegas was 18.5% CO₂-12.1% 02-66.4% N₂-3% H₂O. Tests were performed underaccelerated conditions in terms of temperatures (665° C.) and fuelutilization (80%). Cell resistance, voltage and gas cross-over stabilitywere monitored with the passage of time to evaluate the performance andstability of the electrolyte matrix. The tests were performed at 160mA/cm². FIG. 4 shows the resistance stability comparison between thecomparative electrolyte matrix and the electrolyte matrix of the presentinvention. The inventive electrolyte matrix exhibited greater than 40%improved resistance stability compared to the comparative electrolytematrix. The improvement may be due to fewer large pores being formed inthe matrix and a more stable pore structure as revealed by post-testanalysis. The presence of metal oxide additives eliminated the formationof large pores (>0.2 μm) by reducing/eliminating the coarsening of thematrix particles, which helps to maintain stable capillary force forelectrolyte retention.

In order to evaluate the benefit of the inventive matrix, post-testanalysis were performed on single cells to determine the fraction oflarge pores present in the matrix. FIG. 5 shows an example of the largepore fraction (>0.2 μm) comparison at the end of life between theconventional matrix and the inventive matrix. These results demonstratethat the inventive matrix exhibits a smaller population of large poresand more stable pore structure over time in comparison to conventionalmatrices. The inventive matrix shows a >60% reduction in the populationof large pores (>0.2 μm), confirming the superiority of the inventivematrix over the conventional design.

As utilized herein, the terms “approximately,” “about,” “substantially”,and similar terms are intended to have a broad meaning in harmony withthe common and accepted usage by those of ordinary skill in the art towhich the subject matter of this disclosure pertains. It should beunderstood by those of skill in the art who review this disclosure thatthese terms are intended to allow a description of certain featuresdescribed and claimed without restricting the scope of these features tothe precise numerical ranges provided. Accordingly, these terms shouldbe interpreted as indicating that insubstantial or inconsequentialmodifications or alterations of the subject matter described and claimedare considered to be within the scope of the invention as recited in theappended claims.

The terms “coupled,” “connected,” and the like as used herein mean thejoining of two members directly or indirectly to one another. Suchjoining may be stationary (e.g., permanent) or moveable (e.g., removableor releasable). Such joining may be achieved with the two members or thetwo members and any additional intermediate members being integrallyformed as a single unitary body with one another or with the two membersor the two members and any additional intermediate members beingattached to one another.

References herein to the positions of elements (e.g., “top,” “bottom,”“above,” “below,” etc.) are merely used to describe the orientation ofvarious elements in the Figures. It should be noted that the orientationof various elements may differ according to other exemplary embodiments,and that such variations are intended to be encompassed by the presentdisclosure.

It is important to note that the construction and arrangement of thevarious exemplary embodiments are illustrative only. Although only a fewembodiments have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein. Forexample, elements shown as integrally formed may be constructed ofmultiple parts or elements, the position of elements may be reversed orotherwise varied, and the nature or number of discrete elements orpositions may be altered or varied. The order or sequence of any processor method steps may be varied or resequenced according to alternativeembodiments. Other substitutions, modifications, changes and omissionsmay also be made in the design, operating conditions and arrangement ofthe various exemplary embodiments without departing from the scope ofthe present invention. For example, the heat recovery heat exchangersmay be further optimized.

What is claimed is:
 1. A method of making an electrolyte matrixcomprising: preparing a slurry comprising a support material, acoarsening inhibitor, an electrolyte material, and a solvent; and dryingthe slurry to form an electrolyte matrix, wherein the support materialcomprises lithium aluminate, the coarsening inhibitor comprises amaterial selected from the group consisting of MnO₂, Mn₂O₃, TiO₂, ZrO₂,Fe₂O₃, LiFe₂O₃, and mixtures thereof, and the coarsening inhibitor has aparticle size of about 0.005 μm to about 0.5 μm.
 2. The method of claim1, wherein preparing the slurry comprises an attrition milling processthat reduces the size of the materials in the slurry.
 3. The method ofclaim 1, further comprising tape casting the slurry before drying theslurry.
 4. The method of claim 1, further comprising adding a binder, aplasticizer, a reinforcing material, or a combination thereof to theslurry.
 5. The method of claim 1, wherein the coarsening inhibitor ispresent in an amount of about 0.1 vol. % to about 40 vol. % of drycomponents of the slurry.
 6. A method of making an electrolyte matrixcomprising: forming a mixture of an aluminum containing precursor, alithium containing precursor, and a dopant precursor; drying the mixtureto form a powder; heat treating the powder at a temperature of about550° C. to about 800° C. for a period of about 6 hours to about 30 hoursto form a lithium aluminate including a dopant; preparing a slurrycomprising the lithium aluminate including a dopant, an electrolytematerial, and a solvent; and drying the slurry to form an electrolytematrix, wherein the dopant precursor is in oxide or salt form, and thedopant comprises a material selected from the group consisting of MnO₂,Mn₂O₃, TiO₂, ZrO₂, Fe₂O₃, LiFe₂O₃, and mixtures thereof.
 7. The methodof claim 6, wherein the dopant precursor comprises MnO₂, TiO₂, ZrO₂,Fe₂O₃, or mixtures thereof.
 8. The method of claim 6, wherein thealuminum precursor comprises Al₂O₃.
 9. The method of claim 6, whereinthe lithium precursor comprises lithium carbonate.
 10. The method ofclaim 6, further comprising tape casting the slurry before drying theslurry.
 11. The method of claim 6, further comprising adding a binder, aplasticizer, a reinforcing material, or a combination thereof to theslurry.
 12. The method of claim 6, wherein the lithium aluminateincluding a dopant comprises the dopant in an amount of about 0.1 mol. %to about 15 mol. %.